When to plant
Ensure the tree will have adequate room for growth to maturity. A mature full-sized tree (without pruning for height) can be 20-30 feet tall and equally wide with an extensive root system which can extend up to twice as far as the drip line (the edge of the canopy).
Transplanting from a container to the ground
Handle the tree gently and protect the roots from damage. Dig a hole about twice as wide as the rootball of the tree and about the same depth as the rootball. Save the soil for backfill; break up large clumps. Soil amendments are not recommended unless the soil is extremely sandy or is heavy clay.
Adjust the depth of the hole so that the upper surface of the tree ball is about 1 inch above the surrounding soil. Lower the tree, still in its container, into the hole. Carefully slit one side of the container vertically, then add about 6 to 8 inches of loose backfill (fill the hole about 1/3 full) to stabilize the tree. Then carefully remove the container. Gently tap the loose soil around the rootball immediately, and then promptly fill the rest of the hole with soil, tamping gently as you fill. Fill to the top, leaving the upper 1 inch exposed. Add water directly to the top of the rootball to ensure the roots are kept moist, while keeping the trunk as dry as feasible.
Trees should be planted at the same depth as they were in the container. If planted too deep, soil and water tend to stand against the trunk, which promotes root and crown rots such as Phytophthora. If planted too high, the roots will dry out too quickly.
Young trees with a trunk diameter of less than an inch are especially vulnerable to irrigation issues. Irrigation should be at the root zone area away from the trunk and the bud union to avoid fungal diseases. Newly planted trees should be irrigated well immediately after planting to ensure surface roots stay moist.
There are three basic ways to irrigate citrus trees.
A mature tree with an extensive root system requires more water to wet its larger root zone than a young tree with a smaller root mass. However, the root system of a young tree dries out more quickly.
To ensure good crops, the tree needs adequate nutrition. Nutrient deficiencies reduce yield and adversely affect size, color, sweetness and peel texture of fruit. Typically, nitrogen is the nutrient most often required. In some soils, other minerals may be deficient. A soil analysis can be helpful. A complete organic fertilizer with adequate nitrogen will generally supply the other required nutrients such as iron, zinc, magnesium, phosphorus, potassium.
Young nonbearing trees have different nitrogen requirements than older, bearing trees. In the nonbearing years, the goal is to encourage growth. For the first 1-2 years, apply 2 tablespoons of nitrogen fertilizer 3 to 4 times per year (approximately one-tenth of a pound per year), sprinkling it evenly over the root zone and then watering well. During the third year, the amount of nitrogen fertilizer can be increased to 4-5 tablespoons per application, or approximately one-quarter pound per year. For a 4-year old tree the amount can be doubled again, to 8 tablespoons 3 to 4 times per year (approximately one-half pound per year), applied evenly around the drip line and watered in well.
For older, fully bearing citrus trees of average size, the general recommendation is to apply about 1 pound of nitrogen per tree per year. Depending on the specific fertilizer used the amount to apply can be more than 1 pound. Read and follow package instructions.
Fertilizer should be applied in late winter or early spring, prior to the spring growth period. Fertilizer should not be applied in the summer or fall for oranges and grapefruit to avoid problems with thickening fruit rind. However, lemons benefit from nitrogen fertilizer in the summer months. The fertilizer should be scattered evenly under the tree and at least 1 to 2 feet beyond the drip line, and then watered in well.
Do not apply fertilizer to frost-damaged trees until the full extent of the damage is known. If severely damaged, fertilizing is not recommended until the tree regains the full canopy growth.
Trees in Containers
Using mulch has many benefits to citrus trees. Mulch can be applied as a 2-inch layer on top of the ground underneath the tree, out to beyond the drip line, but at least 6 inches away from the trunk.
Benefits of mulching include:
– Mulch will prevent weed seed germination
– Mulching helps conserve water by reducing evaporation from the soil and reducing runoff, making more water available to the tree
– Organic mulches improve the soil structure and porosity by increasing soil organic matter content over time, especially in the top 12 inches, where citrus roots are most active
– Mulches can reduce the fluctuations in soil temperatures, which is beneficial to root health
– Thick mulches at the soil surface can also suppress growth of some soil organisms such as Phytophthora fungi, which cause root rot
– Yard waste mulch (wood chips, grass clippings, leaves) has been shown to be beneficial for citrus tree growth
Mulch will control weeds so that digging or cultivating under citrus trees can be avoided, as their surface roots are shallow.
Protect from sun
In very hot, sunny areas, protect the trunk and large limbs from sunburn, particularly after pruning that exposes limbs to the sun. Lemons are especially susceptible. Wrap the trunk of a newly planted tree with newspapers or tree wraps and tie loosely. Paint the trunks and exposed limbs of older trees with white, water-based latex paint diluted 1:1 with water.